ignition problem 1987 f150 351 v8 4bbl at,ac
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Junior User
Joined: May 2005
Posts: 67
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From: northern minnesota
ignition problem 1987 f150 351 v8 4bbl at,ac
The problem is when the cranking stops a spark will go across the gap on the testing tool,none during the cranking cycle.the truck will start sometimes then wont alot of the time,this just started last week,please help. I have changed the ignition module,coil,ignition switch,plug wires are new, I am running out of ideas.
Elder User
Joined: Sep 2004
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Get a cheap $4.00 test light. Clip the alligator clip to a good ground. Probe the negative side of the coil primary. Crank the truck. Does the test light flash?
If the answer (to the test light question) is "NO, the test light is always lit" the problem lies in the TFI, Hall Effect Coil, ignition coil, or wiring between them. My money is on the Hall Effect coil in the distributor. If it provides a weak signal, the TFI will sometimes fire and sometimes not; typically the problem will be both voltage and temperature sensitive. And in these circumstances, it is not unexpected that the TFI wouldl fire the coil exactly once as you turn the key off, or go from "crank" to "run".
If the answer(to the test light question) is "YES", then the ignition primary circuit is working, and the problem lies in the ignition coil, high voltage wiring, rotor, distributor cap, etc.
If the answer (to the test light question) is "No, the light is always dark", then there is a problem with the ignition coil or in providing power to the positive side of the coil primary, or your test light is broken. Try probing the positive side of the coil primary. If the light now lights, your coil is bad. If the light is still dark, try probing the battery positive post. If the light now lights, your ignition wiring is bad. If the light does not light, your test light is bad.
If the answer (to the test light question) is "NO, the test light is always lit" the problem lies in the TFI, Hall Effect Coil, ignition coil, or wiring between them. My money is on the Hall Effect coil in the distributor. If it provides a weak signal, the TFI will sometimes fire and sometimes not; typically the problem will be both voltage and temperature sensitive. And in these circumstances, it is not unexpected that the TFI wouldl fire the coil exactly once as you turn the key off, or go from "crank" to "run".
If the answer(to the test light question) is "YES", then the ignition primary circuit is working, and the problem lies in the ignition coil, high voltage wiring, rotor, distributor cap, etc.
If the answer (to the test light question) is "No, the light is always dark", then there is a problem with the ignition coil or in providing power to the positive side of the coil primary, or your test light is broken. Try probing the positive side of the coil primary. If the light now lights, your coil is bad. If the light is still dark, try probing the battery positive post. If the light now lights, your ignition wiring is bad. If the light does not light, your test light is bad.
Thread Starter
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Junior User
Joined: May 2005
Posts: 67
Likes: 0
From: northern minnesota
bear1956
I ended up changing the stator pickup coil inside the dist.thanks for the help.the guy at napa told me i would have to pull the dist.,so i looked at my trusty clymers book and it gave detailed instructions on installing a new one,they also told me that a stator coil is rare in a 87,is this true?
